Facsimile machines (or FAX) were initially designed to transmit and receive data over the Public Switched Telephone Network (PSTN) analog system in accordance with standardized data communication protocols. Frequently used data communication protocols include Group 1 (G1), Group 2 (G2) and Group 3 (G3).
In the PSTN system, these three protocols are traditionally used in a synchronized fashion, where the time interval between image data and command, or the time interval between two commands is pre-determined by the protocols.
FIG. 1 depicts a typical G3 multi-page fax data communication process having changes of image parameters in a normal operation mode over the PSTN system. In FIG. 1, CED stands for Called Station Identification, NSF stands for Non-Standard Facilities, CSI stands for Called Subscriber Identification, DIS stands for Digital Identification Signals, DCS stands for Digital Command Signals, TSI stands for Transmitting Subscriber Identification, CFR stands for Confirmation to Receiver, EOM stands for End of Message, MCF stands for Message Confirmation, EOP stands for End of Procedure, and DCN stands for Disconnect Signal.
In FIG. 1, the blocks at the left hand (calling) side represent a sequence of events performed by a calling machine, while the blocks at the right hand (called) side represent a sequence of events performed by a called machine. This principle also applies to FIGS. 2, 3A-D, 4A-C, 12A-B, and 13A-B.
With reference to FIG. 1, the communication process is initiated by a telephone call from the calling machine. After acknowledging a valid call, the called machine responds with a Non-standard Facilities (NSF) frame. The calling machine then responds with the Non-Standard Setup (NSS) frame, advising the called machine of the resolution and compression for a page of fax data, or a frame of fax data, to follow. If an NSS frame is not received within 3 seconds, the called machine retransmits the NSF frame. A maximum of three NSF tries is attempted before the calling machine signals a failure. On the other hand, once the NSS frame is received, the called machine transmits a Confirmation to Receive (CFR) frame. The calling machine then starts to transmit the fax data page. At the end of the transmission of the fax data page, the calling machine, which is a transmitter, typically transmits an End of Message (EOM) frame within 3.5 seconds. The EOM frame indicates that the calling machine will transmit an additional page of fax data with change of parameters to follow. If the additional page of fax data are to be transmitted without change of parameters, an Multi-Page Signal (MPS) frame is transmitted. If there are no more pages of fax data, an End of Procedure (EOP) frame is transmitted.
With further reference to FIG. 1, after receiving the EOM frame the called machine responds with an Message Confirmation (MCF) frame and transmits an NSF frame to the calling machine within 6 seconds. After receiving both the MCF and NSF frames, the calling machine responds to the called machine by transmitting an NSS frame, informing the called machine of the new parameters for the forthcoming fax data page. The called machine confirms with a CFR frame. The calling machine then transmit the additional page of fax data. At the end of the data transmission, the calling machine transmits an EOP frame, signaling no more image data to transmit. The called machine then returns an MCF frame. Finally, the calling machine transmits the Disconnect (DCN) frame, and the transaction is terminated. As depicted in FIG. 1, the maximum time allowed between two command frames is 6 seconds.
It should be noted that the time schedule in FIG. 1 is exemplary only, since the actual sequence of events and timings varies during each specific facsimile call setup. The actual sequence of events and timings during image data communication also varies with ranges and options specified by the CCITT (International Telegraph and Telephone Consultative Committee).
Even though the synchronized G3 protocol facilitates facsimile data communication over the PSTN system, it does not permit data communication over asynchronous digital data networks. Asynchronous communication is thwarted because the time interval between two command frames, or between a command frame and a data frame, is pre-determined by the G3 protocol.
Specifically, the G3 protocol assumes that, after the transmitting side transmits one page of fax data, the receiving side will process the page of fax data in First In First Out (FIFO) order, within a pre-determined period of time (typically 3 seconds).
As shown in FIG. 1, when a page of fax data has been sent by a G3 transmitting facsimile machine in the PSTN system, an EOM (End of Message) command is sent out 3.5 seconds later. A post message transmission, such as MCF, then is initiated. In the G3 protocol, a RTC (Return To Control) sequence including six EOLs (End of Lines) is embedded at the end of a page of fax data. Consequently, the G3 transmitting facsimile machine typically transmits the EOM command with the assumption that the receiving side has completed processing the received page of fax data, and detected the RTC within 3.5 seconds.
However, in asynchronous digital data networks (such as a closed telephone network using leased lines), delays caused by buffering and multiplexing hardware in the asynchronous digital networks often are found. Thus, it cannot be assumed that the receiving side can complete processing a page of received fax data and the RTC within the pre-determined period of time.
Also, in the PSTN system, after the transmitting side has sent out a command frame, the G3 protocol assumes that the receiving side can respond to the command frame within a pre-determined period of time. If the receiving side fails to respond to the command frame within the pre-determined period of time, the transmitting side typically performs a retry of the command frame.
Further, in G3 protocol, it is possible for either transmitting side or receiving side to send two consecutive command frames with an assumption that the maximum time for processing the preceding command frame will not exceed a pre-determined period of time. For example, the receiver side consecutively generates MCF and NSF command flames within .+-.6 seconds between these two command frames. Without a mechanism to provide positive acknowledgment between calling and called machines, the time period between the two consecutive commands has to be assumed, as in PSTN.
But, in the asynchronous digital data networks, it cannot be assumed that the receiving side can respond to a transmitted command frame within a pre-determined period of time. As noted, no such assumption is warranted due to the delays caused by the asynchronous digital data network hardware.
To adapt facsimile machines to the asynchronous digital data networks, Ricoh Corporation developed an asynchronous facsimile protocol, which is denoted Ricoh IDI (Image Data Interchange) FAX R-2100 protocol (referred to as IDI protocol hereinafter). The IDI protocol achieves compatibility with a large number of existing asynchronous digital data networks while retaining the features and conventions of the widely accepted G3 facsimile terminals.
The IDI protocol successfully adds a mechanism to the G3 protocol to compensate for the delays caused by hardware in the asynchronous digital data network, e.g., buffering and multiplexing hardware. To adapt the IDI protocol, Ricoh Corporation also developed a model of facsimile machines (called R-2100 facsimile machines). The IDI protocol successfully connects R-2100 facsimile machines to the asynchronous digital data networks.
"Negotiation" refers to a bilateral information exchange between a calling facsimile machine and a called facsimile machine. A typical facsimile image may include the information that defines various image parameters, such as data compression technique, resolution, tolerance, scan line length, scanning direction, scanned line transmission time, contrast levels, etc.
Specifically, the G1, G2, and G3 protocols provide low, medium, and high resolutions (or scanning densities). The low resolution provides 3.85 lines per mm (vertical) by 864 picture elements along the horizontal scan line (or 100 by 100 lines per inch). The medium resolution provides 3.85 lines per mm (vertical) by 1728 picture elements along the horizontal scan line (or 100 by 200 lines per inch). The high resolution provides 7.7 lines per mm (vertical) by 1728 picture elements along the horizontal scan line (or 200 by 200 lines per inch).
The G3 protocol further provides two coding schemes both a one-dimension coding scheme, and a two-dimension coding scheme. The one-dimension coding scheme is essentially Modified run-length Huffman Code (MH), while the two-dimension coding scheme is essentially Modified Relative Element Address Designate (READ) Code (MR).
A typical facsimile machine may have limited capabilities to adapt to specific configurations of these parameters. Thus, a negotiation process can be used to determine parameters suitable to the capabilities for both the calling facsimile and the called facsimile machines, thus facilitating fax data transmission.
Unfortunately, IDI protocol does not provide a mechanism to perform such negotiation. As a result, even though R-2100 model facsimile machines can efficiently communicate with each other over the asynchronous digital data network in accordance with IDI protocol, they lack negotiation capability.
As a result, under the IDI protocol, the transmitter operates as a master, driving the receiver to accept the resolution and compression technique set at the transmitting side. The Non-Standard Setup frame (NSS) transmitted by the transmitter commands the receiver regarding the resolution and compression to be utilized in the subsequent transmitted fax data. The receiver accordingly adjusts itself to accept the fax data.
Initially, when IDI protocol was first developed, lack of negotiation capability did not cause problems because Ricoh Corporation was the only manufacturer to produce asynchronous protocol adaptable facsimile machines (R-2100 facsimile machines). When only one model of asynchronous protocol adaptable facsimile machines is available in the market, these facsimile machines can properly communicate with each other, even without negotiation capability. Subsequently, Ricoh Corporation produced (and continues to produce) new models of facsimile machines that can adapt to the asynchronous facsimile protocol. Other manufacturers have followed Ricoh Corporation's asynchronous facsimile protocol, and also have produced facsimile machines that adapt to the asynchronous facsimile protocol. Without negotiation capability, facsimile machines will encounter problems when communicating with facsimile machines of different models. Further, newer facsimile protocols, such as Group 4 (G4) protocol, have more features than G1, G2 and G3 protocol. Without negotiation capability, it is difficult to incorporate desirable new features into asynchronous facsimile protocols.
Even with a negotiation capability, it is important to identify and perform error correction in an asynchronous environment. In a noisy data transmission environment such as an asynchronous digital data network, it is particularly important to incorporate some form of error detection and correction during transmission.
Thus, there is a need to provide facsimile machines with negotiation capability including error detection and correction, and to provide an associated method, that adapts to an asynchronous facsimile protocol. This invention provides such facsimile machines and method.